Philips 204U, 1941

Description: These very small sets have an interesting design
history. Originally a Philips design, it was "acquired"
for production in several German factories during the first years of WWII,
under a number of designations, but with basically the same appearance and
circuits and parts. The tubes are from the newly developed 20 series by
Philips, of small size, using a "loktal" socket (like in the
US), but using the center "chimney" also as a connection.
Miniaturization of many parts allowed a radio to be built that had
excellent performance. The radio on top was manufactured by NSF
(Nederlandse Signalbau Fabriek, I believe), a close associate to the
Philips firm. The bottom one was made by Philips Aachen (Germany),
most likely during WWII. The basic design was made in three variants: the 203U
with Medium and Long waves, the 204U with Medium and Short waves and the
208U with Long, Medium and Short waves. The oscillator and
converter is a UCH21 tube, a triode-hexode. This is followed by
another UCH21 working as IF amplifier (the hexode section) and Audio
preamplifier (the triode). Then, a UBL21, double diode-power pentode
does the detection and AGC voltage generation and the power output.
The half-wave rectifier is a UY21 in these sets. Other variants used a
UY1N, a very similar tube, but with octal socket. The Aachen version
has slats for ventilation on the top of the case, something very much
needed in the other radio.

The circuit of the radios were designed with economy
in mind, the number of parts is smaller than one is accustomed to seeing
in European radios of the late 30's. The volume control, for
example, provides not only its main function of changing the audio drive
to the triode preamplifier, but it also carries the DC bias for that
triode, derived from the AGC. For that reason, as the potentiometer
becomes old, the typical scratching when changing volume has become a
powerful noisy scratch that is not easy to overcome. Sprays perhaps have
helped a bit, but not much. The adjustment of the IF transformers
seems devilish to me. There are two intertwined soldered coiled
wires that carry a magnetic core at their tips and are placed in the
center of the IF transformer tube. Presumably, shortening or
lengthening the wires changes the adjustment of the transformers. I have
not wanted to mess around with that in these radios. They work pretty
well as they are, particularly with the new Philips and Mullard tubes I have
installed. The condition of the UBL21 is rather critical to
performance. The power pentode section is not terribly important, but the
double diodes are. As the tube ages, it seems that the detection
process is severely handicapped before the power pentode weakens
noticeably. I am using them at 117 Volts, although they perform better
at 220 with an
up-transformer, but I do not want to stress the components too much.

Source: Both sets came, at different times, from my friend Lutz-Dietmar Schmidt in Berlin,
Germany.

Date acquired: November 2001 (NSF) and 2007 (Philips
Aachen)

Initial Price: 190 DM, plus shipping for the NSF.

Schematic: In my files

Condition: Both cabinets are in rather nice
condition. I had to change a number of capacitors and all the tubes,
although the original ones still played. The potentiometer of the
NSF scratches loudly, but it is OK once set to the desired
volume. The potentiometer of the Aachen does not scratch, and it has
a different construction. The back cover of the NSF is not for this particular set, but for a
208U. The cover for the Aachen is correct for a 204U, but the
chassis is a bit peculiar. It appears to be correctly a 204U, except
that it has an intermediate position in the band switch which is in the
wrong position, if one is to trust the dial plate indications. There are
coils for the intermediate position, but I have not been able to determine
whether it is Long Wave, in which case it would be a 208U. The power
resistors of both radios have been partially replaced, as they were
damaged. The tone quality of the approximately 5" speaker is
remarkably good for its size. It should be noted that these sets work
rather nicely when they work, but they can fail very easily because of the
sockets that are used. The metal that makes contact with the tube pins
becomes easily dirty or corroded, particularly the cathode connections,
done through the central chimney. Repairs and part exchanges are
also quite difficult. None of the electrolytic capacitors are
original, although I have left their cans in place.